MIAMI -- Reds closer Aroldis Chapman threw 40 fastballs of long toss from 40-50 feet before batting practice on Friday as he tries to return to the bullpen.
Chapman is battling fatigue in his left arm, which began to bother him two outings ago.
"I feel a lot better," he said. "I think a few more days, I'll be good."
On Monday, he walked two batters on nine pitches before being removed in the middle of the inning. Chapman allowed four hits, including Matt Dominguez's three-run homer, in last Friday's loss to the Astros.
The 24-year-old southpaw said that he has felt this two or three times before in his career, the last of which came in 2011. He is 17 2/3 innings over his career high in innings pitched.
"There's a long season and sometimes you forget about continuing to do some exercises and you get fatigued," Chapman said.
Through 64 games, Chapman is 5-5 with a 1.60 ERA and 119 strikeouts in 67 2/3 innings. His 35 saves are tied with Atlanta's Craig Kimbrel for the National League lead.
"I wish this would've happened earlier in the season, because this is the time of the season when we're on the final [stretch] of the season and I would like to be better," Chapman said.
Stubbs studies Marlins Park's outfield quirks
MIAMI -- Reds center fielder Drew Stubbs took extra time before and during batting practice on Friday to acclimate himself with the spacious confines of Marlins Park.
"BP is about getting your bearings for where the walls are at and your daily routine of taking balls off the bat," Stubbs said. "Give you a feel for how the ballpark plays."
While Stubbs walked around the outfield to get a feel for his territory, the retractable roof was open. During batting practice and the game, it was closed.
Straightaway center stands 418 feet from home plate. The right-center gap reads 392 feet. The home-run sculpture in left-center creates a tricky curve in the wall.
"It's a big ballpark and outfield play is going to be pretty essential to success here," said Stubbs, who has four errors and five assists in 109 starts in center. "Hopefully, we can hold down."
The Reds became the final National League team to visit Marlins Park this season. Cincinnati went 39-35 at Miami's old home.
"It's exciting to have a new setting and see what it's like," Stubbs said.
Baker mixing and matching to keep guys fresh
MIAMI -- Reds manager Dusty Baker continues to mix and match his lineup with players on the mend.
Todd Frazier started Friday night's game at third base for Scott Rolen, who played the last two games in a sweep of the Pirates. Rolen missed a week dealing with two disk protrusions in his lower back.
"Frazier's been out a couple of days, I figured that was long enough," Baker said. "Just mixing and matching, trying to keep everybody sharp and not letting guys go too long without playing."
Zack Cozart, who is battling a left oblique strain, hasn't played since Sept. 3. He hit off a tee, but has yet to hit live pitching. The 27-year-old has taken grounders.
Wilson Valdez received the nod at shortstop for the sixth time in the past eight games.
"Zack's doing pretty well," Baker said. "That oblique, he has to be really careful with that. We're taking our time, and had a long talk with him last night. We're hoping soon, we just don't know when."
Christina De Nicola is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.